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An unmanned supply rocket bound for the International Space Station has exploded during its launch from the US state of Virginia.

Antares, a 14-storey rocket built by Orbital Sciences Corp, combusted seconds after leaving the seaside launch pad at Wallops Flight Facility.The cause of the cargo ship malfunction has yet to be determined.The initial planned launch of the spacecraft on Monday was delayed due to a sailboat in nearby waters.The flight was expected to be the third contracted mission with the National Aeronautics and Space Administration.The rocket was due to carry nearly 5,000 pounds (2,200kgs) of supplies to six astronauts aboard the International Space Station."We will understand what happened, hopefully soon, and we'll get things back on track," said Frank Culbertson, executive vice-president of Orbital Sciences. "We've all seen this happen in our business before, and we've all seen the teams recover from this, and we will do the same."

The rocket just before take-off

No-one was injured, said Mr Culbertson, and an investigation team was already going through the data to try to establish the cause.On Wednesday morning, he said, the examination of debris around the site would begin.The investigation will not jump to conclusions but one line of inquiry will surely focus on the AJ-26 engines used to lift the rocket away from the pad, says BBC science correspondent Jonathan Amos."These are actually modified Russian-built power units that were originally developed for the ill-fated Soviet Moon rocket, the N-1. "They have been refurbished to modern standards, but one blew up in ground testing earlier this year."

Flames shot into the air during launch

Analysis: Jonathan Amos, BBC science correspondent This new rocket was part of Nasa's effort to contract out "routine" cargo resupply to the International Space Station. But if we needed reminding that nothing in space is routine then this explosion has brought that message home in spectacular fashion. The US space agency "seeded" development of Antares - and the supply ship it launches, Cygnus - by giving incentive payments to manufacturer Orbital Sciences Corporation, to help them develop a low-cost, commercial follow-on to fill the cargo gap left by the retired space shuttles. The blast is likely to have seriously damaged the launch pad and support infrastructure, meaning that even if the fault is quickly identified and corrected, restarting Antares flights again may take a long time. However, there should be no immediate threat to supplies for astronauts on the space station. The Cygnus cargo ship that was on top of the Antares is one of a fleet of vehicles that are used in this role. These other robotic vessels, launched atop other rockets, will now have to pick up the slack. There is no doubting the explosion is a major setback for Orbital Sciences Corporation, and its plans to market Antares as a multi-purpose, commercial launcher. Confidence always takes a hit in the wake of a failure. But Orbital has the expertise to come back - as it has done after previous launch failures.